Ultraviolet irradiation increases serum 1,25-dihydroxyvitamin D in vitamin-D-replete adults.

The production of vitamin D metabolites in response to ultraviolet irradiation has been studied in 5 control subjects and 8 patients with psoriasis; both groups responded similarly. Significant increases within the normal range were observed for serum 1,25-dihydroxyvitamin D; these increases were negatively related to the initial concentrations of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D. Serum 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D increased linearly over the 21 days of study, the production of 25-hydroxyvitamin D being negatively correlated with its own initial concentration. The changes in vitamin D metabolism were accompanied by significant rises within the normal ranges in serum inorganic phosphorus and in urinary calcium. These results indicate the variation of 1,25-dihydroxyvitamin D occurs in vitamin-D-replete adults and that this variation is probably responsible for the observed alterations in calcium and phosphorus metabolism.